This invention relates generally to ultrasound application in diagnosing bladder dysfunction.
A variety of techniques have been used to evaluate bladder dysfunction. Such techniques typically attempt to determine the size of the bladder or bladder volume, meaning the amount of urine in the bladder. As one example, U.S. Pat. No. 6,110,111 to Barnard discloses a system for assessing bladder distension by using ultrasound to compare the bladder surface area with the surface area of a sphere. According to Barnard, the closer the bladder is to a spherical shape, the greater the pressure within the bladder.
Bladder mass measurements can also be used to diagnose several different clinical conditions. Bladder wall thickness and bladder mass can be used to indicate bladder outlet obstruction and bladder distension. An outlet obstruction will cause a higher pressure in the urine, against which the bladder muscle must contract. That higher pressure causes the muscle to exert more force, resulting in hypertrophy of the bladder muscle. Symptoms of bladder muscle hypertrophy include increased wall thickness and increased mass. The use of bladder wall thickness as an indicator of detruser hypertrophy has been noted for many years (see Matthews P N, Quayle J B, Joseph A E A, Williams J E, Wilkinson K W, Riddle P R, The use of ultrasound in the investigation of prostatism, British Journal of Urology, 54:536-538, 1982; and Cascione C J, Bartone F F, Hussain M B, Transabdominal ultrasound versus excretory urography in preoperative evaluation of patients with prostatism, Journal of Urology, 137:883-885, 1987). Converting bladder wall thickness to bladder wall volume (or bladder mass by multiplying bladder wall volume by the specific gravity of bladder tissue) yields a single number, which is independent of bladder volume. While the bladder wall thins as volume increases, the total bladder wall volume (or bladder mass) remains unchanged.
Another key parameter of bladder functionality is bladder distension. As the bladder volume and bladder pressure increases, the bladder walls stretch and thin. Two prominent maladies associated with bladder distension are incontinence and hyperdistension.
Incontinent episodes frequently occur if the bladder sphincter muscles are unable to retain urine as bladder pressure and bladder distension increases. In many individuals this incontinent point occurs at a consistent volume. Consequently, if this volume is known and if the bladder volume can be measured over time, then incontinent events can be prevented. Furthermore, research has shown that it is possible to increase both the bladder capacity and the bladder volume incontinent point through a variety of methods. This technique has been used effectively on enuretic patients.
Hyperdistension refers to the case in which the bladder is allowed to fill to such an extreme that excessive bladder pressure builds which can cause potential renal damage, renal failure and even patient death from autonomic dysreflexia if the patient has spinal cord damage. As with incontinence, hyperdistension has been successfully prevented using non-invasive bladder volume measuring.
At small bladder volumes, bladder response is quite constant across humanity. Normal adult humans typically have no trouble voiding and leaving less than 50 ml of urine. Thus it has been relatively easy to establish post-void-residual (PVR) volumes that are normal and PVR volumes that are potential medical problems. At low bladder volumes bladder distension information is not as useful. However, normal humans have widely variant bladder capacities. Thus it is more difficult to establish a volume threshold at which over-distension occurs or when incontinence occurs. As the bladder fills, quantization of bladder distension becomes more useful. This is especially true since it is thought that a bladder distension metric would better indicate hyperdistension and bladder capacity.
Current methods to measure bladder wall thickness rely on one-dimensional (A-mode) and two-dimensional (B-mode) ultrasound and are greatly susceptible to operator error, time consuming, and inaccurate. The operator using one or two-dimensional ultrasound has to repeatedly reposition the ultrasound probe until a bladder wall image is sufficiently visible, usually the more anterior portion of the bladder. Furthermore, the limitations of one and two-dimensional ultrasound require inaccurate spherical model assumptions for the bladder. Presumably for these and other reasons the industry has concluded that measuring bladder wall thickness is an unreliable or ineffective means to quantize bladder distension. See, e.g., Barnard, U.S. Pat. No. 6,110,111 at column 1, lines 50-59.
Thus, there is a need for a system to accurately measure bladder wall thickness for use in evaluating bladder distension.
The present invention incorporates a three-dimensional ultrasound device to scan a patient""s bladder. Data collected in the ultrasound scan are then analyzed to calculate bladder mass. Bladder mass information is then used to assess bladder dysfunction.
In accordance with the preferred embodiment of the invention, a microprocessor-based ultrasound apparatus, placed on the exterior of a patient, scans the bladder of the patient in multiple planes with ultrasound pulses, receives reflected echoes along each plane, transforms the echoes to analog signals, converts the analog signals to digital signals, and downloads to the digital signals to a computer system.
Although a variety of scanning and analysis methods may be suitable in accordance with this invention, in a preferred embodiment the computer system performs scan conversion on the downloaded digital signals to obtain a three-dimensional, conically shaped image of a portion of the bladder from mathematical analysis of echoes reflecting from the inner (submucosal) and outer (subserosal) surfaces of the bladder wall. The conical image is obtained via three-dimensional C-mode ultrasound pulse echoing using radio frequency (RF) ultrasound (approximately 3-10 MHz) to obtain a regularly spaced array of multiple scanplanes, each scanplane including regularly spaced multiple scanlines. The combination of regularly spaced scanplanes results in a solid angle scan cone that provides a basis to locate bladder wall regions or surface patches of the inner and outer surfaces of the bladder wall. The location of each surface patch is determined using fractal analytical methods and the distance or thickness between the inner and outer surface patches is measured. The bladder wall mass is calculated as a product of the surface area of the bladder, the bladder wall thickness, and the specific gravity of the bladder wall. The entire bladder wall or various regions, including anterior, posterior, and lateral portions of the bladder, may be measured for thickness and mass.
An alternate embodiment of the invention configures the downloaded digital signals to be compatible with a remote microprocessor apparatus controlled by an Internet web-based system. The Internet web-based system has multiple programs that collect, analyze, and store organ thickness and organ mass determinations. The alternate embodiment thus provides an ability to measure the rate at which internal organs undergo hypertrophy with time. Furthermore, the programs include instructions to permit disease tracking, disease progression, and provide educational instructions to patients.